When fine-grained or pulverulent bulk materials are removed from pressurized containers, the gas which escapes from the lock chamber as the latter is pressure-relieved will entrain fine material.
That undesired discharge of the solids can be prevented by filling the lock chamber only in part so that a stilling or quieting space is disposed above the bulk material and solids entrained from the bulk material, in response to a pressure relief, can be collected in this stilling space.
Alternatively, the lock chamber may be very gradually relieved of pressure so that gas will flow only at a low velocity in the chamber.